1. Field of the Invention
This invention relates to neural tissue stimulation and infusion techniques, and more particularly relates to such techniques for treating various disorders, including movement disorders.
2. Description of Related Art
Patients with neurodegenerative diseases or trauma like cerebral infarct or spinal cord injury can have a variety of movement and muscle control problems, like resting, postural, intention or action tremor; dystonia (improper muscle tone); spasticity (undesirable movements, or muscle co-contraction); dyskinesia (poorly executed movements) or involuntary movements like ballismus, choreiform movements and torticollis (inappropriate movements or limb control). Many of these problems can be called hyperkinesia. Although they can be chronic, or worse, progressive, they also may have times of relative remission. Such problems are found, at certain stages, for patients with Parkinson's disease, multiple sclerosis, cerebral palsy, secondary to deafferentation pain, post stroke, post apoplexy or anoxia, post head or spinal trauma, post poisoning, cerebellar disease, etc. Dyskinesia also may result from long term usage of levodopa or other drugs, especially for Parkinson's patients.
Spasticity is defined as a state of excessive muscular tonus (hypertonus) and increased spinal reflexes. This condition exists when the corticospinal pathways have been disrupted. Disruption can occur as a result of stroke causing injury to the fibers as they pass through the internal capsule, a degenerative disorder or physical trauma to the cortex or spinal cord. Loss of this pathway leads to a lack of inhibition of the lower motorneurons which then are more active and responsive to reflexes. In some cases injury to the premotor cortex disrupts the output of the primary motor cortex leading to the similar phenomena.
One form of the Dyskinesia is known as Ballism which typically results in violent flinging movements of the limbs. The movements often affect only one side of the body, in which case the disorder is known as Hemiballism.
In patients suffering essential tremor or tremor due to Parkinson's Disease, the predominant symptom of the disordered movement is tremor. Tremor is often subdivided on the basis of whether the trembling of the limb occurs when the limb is at rest or when muscular contraction is occurring.
Besides being caused by degenerative illness or head injury, tremor can be of unknown origin. One syndrome of idopathic tremor is referred to as essential tremor.
Patients with neurodegenerative diseases or trauma to the basal ganglia like cerebral infarct can have a variety of movement and muscle control problems, like akinesia (impairment in movement initiation), rigidity (stiffness, inflexibility, immobility) or bradykinesia (reduction in amplitude and velocity of movement). These motor disorders may be classified as hypokinetic problems, reflecting an abnormal reduction in voluntary movement. These problems can be chronic, or worse, progressive, but they also may have times of relative remission, especially when drugs are effective. Such problems are common, at certain stages, for patients with Parkinson's disease multiple sclerosis, cerebral palsy, secondary to deafferentation pain, post stroke, post apoplexy or anoxia, post head or spinal trauma, post poisoning, cerebellar disease, etc. Dyskinesia is often a side-effect from medications used for certain symptoms (like tremor, akinesia, rigidity), especially levodopa.
Neurosurgeons have been able to diminish the symptoms of the foregoing movement disorders by lesioning certain brain areas. In addition, it has been demonstrated that open-loop Deep Brain Stimulation (DBS) at high frequencies (100 Hz. or higher) of certain brain structures can alleviate, diminish, or completely stop symptoms of tremor, rigidity, akinesia or hemiballism. Published targets of stimulation include the VIM (ventral intermediate thalamus), subthalamic nucleus, and internal globus pallidus.
It is believed that many symptoms of the foregoing motion disorders are due to dysfunction of the basal ganglia or thalamus. The dysfunction can result in overactivity of the output neurons of the ganglia creating excessive inhibition of the thalamus or underactivity of the ganglia resulting in too little inhibition of the thalamus. If there is too little output activity from the basal ganglia or too little inhibition of the thalamus, a condition such as Ballism or Dystonia will result. If there is too much output activity from the basal ganglia (too much inhibition), a condition such as Hypokinesia will result.